Traditional data centers use redundant array of independent disks (RAID) storage technologies to store data to hard disk drive (HDD) storage media. These HDD storage media include spindles that rotate platters at high spinning speeds when the HDD storage media are integrated into the RAID storage system. The high spinning speeds are maintained throughout the operation of the HDDs for the HDDs to remain accessible for read and write I/O by the storage system and hosts.
Conventionally the HDDs may have spin speeds in excess of 7,000 rotations per minute (RPMs) or 15,000 RPMs, depending upon the technology used. Generally, higher spin speeds correspond to faster I/O performance due to shortened seek and access times. However, the power consumption of the HDDs also increases at higher spin speeds. For data centers that have a large number of HDDs (for example, millions of HDDs), power consumption may be a significant cost.
One HDD technology that is available to target the power consumption problem is HDD technology that provides a sleep mode. In sleep mode, the spindle motor of an HDD may be powered down to reduce power consumption. This technology has been used by technology centers to allow the data centers to provide two hard drive states: full speed and spun down (not spinning). However, while in the spun down state, I/O cannot be performed on the HDD. Thus, to access data from the HDD, the spin speed of the HDD must be increased from the not spinning state to the full speed, which may cause delays that adversely affect performance.
Therefore, a need exists for systems and techniques to make efficient use of the power savings and other improvements offered by reducing the spin speeds of HDDs, while maintaining the processing advantages of spinning the HDDs at full spin speeds. In particular, systems and methods that vary HDD spin rates without significantly impacting performance would provide a valuable improvement over conventional storage systems. Thus, while existing storage systems have been generally adequate, the techniques described herein achieve higher energy efficiency while maintaining performance.